Hi Itamar,
I'm all for the solution with the button. Building aligned lists for dbs is something that has taken a terrible amount of time every time it had to be done (no matter how versed one is in HTML), and there's no way around it if you want a decent looking database. At the same time, I don't think it would be worthwile (possible?) to "teach" a single editor instance on the template page to accept incomplete HTML-tags.
I find the button solution an elegant way to tackle this, and as long as the button behaviour is "parallell" to the "reset template" button, I don't think we'd need additional warnings.
A lot of interest from my side 